HP-UX Reference (11i v3 07/02) - 3 Library Functions A-M (vol 6)

f
fopen(3S) fopen(3S)
NAME
fopen(), freopen(), fdopen() - open/reopen a stream file or convert file to stream
SYNOPSIS
#include <stdio.h>
FILE *fopen(const char *__restrict pathname, const char *__restrict
type);
FILE *freopen(const char *__restrict pathname, const char *__restrict
type, FILE *__restrict stream);
FILE *fdopen(int fildes, const char *type);
DESCRIPTION
fopen() Opens the file named by pathname and associates a stream with it.
fopen() returns a
pointer to the
FILE structure associated with the stream.
freopen() substitutes the named file in place of the open stream. The original stream is closed,
regardless of whether the open ultimately succeeds.
freopen() returns a pointer to
the FILE structure associated with stream and makes an implicit call to clearerr()
(see ferror(3S)). After a successful call to freopen() , the orientation of the stream is
cleared (see orientation(5)).
freopen() is typically used to attach the preopened streams associated with stdin,
stdout, and stderr to other files.
fdopen() associates a stream with a file descriptor. File descriptors are obtained from open(),
dup(), creat(),or pipe() (see open(2), dup(2), creat(2), and pipe(2)), which open
files but do not return pointers to a
FILE structure stream. Streams are necessary input
for many of the Section (3S) library routines. The type of stream must agree with the mode
of the open file. The meanings of type used in the fdopen() call are exactly as specified
above, except that w, w+, wb, and wb+ do not cause truncation of the file.
pathname Points to a character string containing the name of the file to be opened.
type Character string having one of the values listed below. The b in the following values has
no effect. It exists to distinguish binary files from text files; however, there is no distinction
between these types of files on UNIX systems (it is required for ISO C standard confor-
mance).
r or rb open file for reading
w or wb truncate to zero length or create file for writing
a or ab append; open file for writing at end of file, or create file or writing
r+, rb+,orr+b open file for update (reading and writing)
w+, wb+,orw+b truncate file to zero length or create file for update
a+, ab+,ora+b append; open or create file for update at end-of-file
When a file is opened for update, both input and output can be done on the resulting stream. However,
output cannot be directly followed by input without an intervening call to fflush() or to a file position-
ing function (fseek(), fsetpos() ,orrewind()), and input cannot be directly followed by output
without an intervening call to a file positioning function unless the input operation encounters end-of-file.
When a file is opened for append (that is, when type is a, a+, ab+,ora+b), it is impossible to overwrite
information already in the file. All output is written at the end of the file, regardless of intervening calls to
fseek(). If two separate processes open the same file for append, each process can write freely to the file
without fear of destroying output being written by the other. Output from the two processes will be inter-
mixed in the file in the order in which it is written.
Notes
HP-UX binary file types are equivalent to their non-binary counterparts. For example, types r and rb are
equivalent.
462 Hewlett-Packard Company − 1 − HP-UX 11i Version 3: February 2007